1. Field of the Invention
The present invention generally relates to semiconductor-processing, particularly to a method for supplying a gas over a substrate with a flow rate gradient in parallel to the substrate, e.g., in a UV irradiation chamber.
2. Description of the Related Art
In film deposition processes or film treatment processes in manufacturing semiconductor devices, reaction gas or purge gas is required to be supplied uniformly over a substrate to be processed in order to process the substrate uniformly with respect to in-plane uniformity. For this purpose, conventionally, by installing a showerhead in an upper part of a reaction chamber facing a substrate, gas is supplied uniformly therefrom toward the substrate. However, in processes such as those where a substrate to be processed is irradiated uniformly with UV light for curing a low-k film formed on the substrate, for example, a showerhead cannot be installed in an upper part of the reaction chamber. In such processes, reaction gas or purge gas is required to be supplied to the reaction chamber from side walls of the reaction chamber. For example, typically two types of gas supply are used. FIG. 1 illustrates one of the types where gas is supplied from a side wall opposite to an exhaust duct inside the reaction chamber, thereby forming laminar flow of the gas over the substrate. FIG. 2 illustrates the other type where gas is supplied from the whole circumference surrounding the outer periphery of the substrate toward the center, and discharged from the circumference of the reaction chamber.
In the former type, because a gas runway over the substrate is long, gradients of substrate temperature and concentration of byproducts are created in a direction from the upstream side to the downstream side, so that uniform processing becomes difficult. In the latter type, since a gas runway over the substrate is short, the substrate temperature can be uniform. However, when gas flow increases, gas flow is centralized at the center, and thus, the substrate temperature near the center may become lower than that of the other parts of the substrate. Further, the centralized gas tends to stagnate at the center, and thus, byproducts or floating particles or foreign objects are not easily discharged and tend to accumulate at the center, causing contamination or creating impurities.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.